A mathematical model of cocoa bean fermentation

Abstract

Cocoa bean fermentation relies on the sequential activation of several microbial populations, triggering a temporal pattern of biochemical transformations. Understanding this complex process is of tremendous importance as it is known to form the precursors of the resulting chocolate’s flavour and taste. At the same time, cocoa bean fermentation is one of the least controlled processes in the food industry. Here, a quantitative model of cocoa bean fermentation is constructed based on available microbiological and biochemical knowledge. The model is formulated as a system of coupled ordinary differential equations with two distinct types of state variables: (i) metabolite concentrations of glucose, fructose, ethanol, lactic acid and acetic acid and (ii) population sizes of yeast, lactic acid bacteria and acetic acid bacteria. We demonstrate that the model can quantitatively describe existing fermentation time series and that the estimated parameters, obtained by a Bayesian framework, can be used to extract and interpret differences in environmental conditions. The proposed model is a valuable tool towards a mechanistic understanding of this complex biochemical process, and can serve as a starting point for hypothesis testing of new systemic adjustments. In addition to providing the first quantitative mathematical model of cocoa bean fermentation, the purpose of our investigation is to show how differences in estimated parameter values for two experiments allow us to deduce differences in experimental conditions.

Dissecting industrial fermentations of fine flavour cocoa through metagenomic analysis

“…LABs are recognized as a crucial group of microorganisms in cocoa fermentations 30 . Our data revealed a higher abundance of these microorganisms at both farms during the first 3 days of fermentation, as reported in the literature 28 , 29 . The ability of LAB to transform pulp’s fermentable sugars and citric acid into lactic acid, mannitol, and pyruvate has been previously described 31 .…”

“…At both farms, the relative abundance of AAB was observed to increase over fermentation (Fig. 3 ) as previously reported 28 , 29 .

Figure 3 Relative abundance of selected microorganism groups sharing common metabolic and physiological characteristics during the fermentation of fine flavour cocoa beans.

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“…2 ). Our data revealed a decrease in bacterial and fungal diversity during fermentation at both farms, which is concomitant with the reported production of typical metabolites affecting microbial growth such as ethanol and weak acids 29 and the observed changes in beans mass temperature (Supplementary Fig. S1 ).…”

“…5 H). This behaviour has been associated with the production of inhibitory weak acids during the last days of fermentation 28 , 29 . Surprisingly, the abundance of Saccharomyces cerevisiae at Necoclí farm was always higher throughout the fermentation step (Fig.…”

Formation of aromatic compounds precursors during fermentation of Criollo and Forastero cocoa

“…In the case of cocoa, there have been some attempts to study the transition of the microbial population in heap fermentation, but there are no detailed studies of its kinetics (Ghosh, 2016). Recently (Moreno-Zambrano et al., 2018), has constructed a mathematical model using ordinary differential equations with two distinct types of state variables: (i) metabolite concentrations of glucose, fructose, ethanol, lactic acid and acetic acid and (ii) population sizes of yeast, LAB and AAB. However, it is worth mentioning that the spontaneous fermentation process will be specific for each batch of cocoa, therefore it will be necessary to develop a controlled fermentation that is a standard reference for the batches and thus be able to produce cocoa of the most uniform quality possible.…”